The present invention relates to an alternating current motor drive circuit which drives an alternating current motor, using an alternating current generator and a direct current power source capable of a power supply and absorption, and to an electric vehicle drive circuit using the drive circuit.
FIG. 10 is a circuit diagram showing a first conventional example of an alternating current motor drive circuit as shown in JP-A-2004-112883, in which a three-phase output of an alternating current generator M2 is converted into a direct current by a voltage source rectifier 31 in which arms having switching elements connected in inverse parallel to diodes are bridge-connected, and the voltage of the direct current is smoothed by a capacitor 13. Also, a direct current chopper 12 is provided between the smoothed direct current (connection points N1 and N2) and a battery B, and a power exchange between them is carried out. Furthermore, using the direct current, an alternating current motor M1 is driven by a voltage source inverter 14 in which arms having switching elements (Q3 to Q8) connected in inverse parallel to diodes (D3 to D8) are bridge-connected.
Meanwhile, as an example in which an output of an alternating current generator is directly converted into an alternating current by a matrix converter, and fed to an alternating current motor, a circuit shown in FIG. 11 is also known as described in JP-A-2005-318731. FIG. 11 is a circuit diagram showing a second conventional example, realizing a power conversion between motor generators MG1 and MG2, using a matrix converter 38. Furthermore, in order to exchange power with a battery 12, a voltage source inverter 36 and a direct current chopper 32 are provided.
In the meantime, in FIG. 10, a large-capacity version of the capacitor 13 is needed for smoothing a direct current, it is difficult to downsize the circuit. Also, a reactor L1 is needed in the direct current chopper 12, there is a problem in that the circuit becomes larger due to this too.
Meanwhile, also in FIG. 11, a large direct current capacitor C2 is needed between the battery 12 and the motor generator MG2, it is difficult to downsize the circuit. Also, a reactor L1 is needed in the direct current chopper circuit 32, there is a problem in that the circuit becomes larger due to this too.
Accordingly, although not otherwise specified as being for an electric vehicle, the circuit shown in FIG. 12 is also proposed in the paper entitled “A Control Method of AC and DC Power Supply Direct Interface Converters”, Institute of Electrical Engineers of Japan, The Papers of Technical Meeting on Semiconductor Power Conversion SPC-06-155, pp. 51-55. FIG. 12 is a circuit diagram showing a third conventional example, and this circuit can be used when a battery voltage is lower than a direct current link voltage. In the circuit of FIG. 12, a direct current link capacitor is omitted, but a reactor is connected. In this circuit a reference potential of a battery is a negative side potential of the direct current link, and the battery is not connected to a neutral point of a motor or generator.
Consequently, it would be desirable to particularly eliminate a need for a reactor in a direct current chopper, and achieve a downsizing of the circuit